Cactus don't like to grow sideways like that. LOL
Cactus is an amazing plant, it can survive 115 degrees F hot blister full sun all summer and blizzard cold winter weather conditions all winter but they grow best at about 70 to 75 degrees with full sun all morning the coolest part the the day then shade from about 11 am the rest of the day until dark.
There are 2 kinds of cactus, low elevation hot dry weather hot dry cactus that only get a small rain about twice per year and higher elevation cactus that get lots of rain or snow melt. If you have a dry weather cactus too much water will kill it. If you have wet weather cactus too much water will not hurt it unless soil holds water like a swap. You need sandy well drained soil.
Desert soil has almost no food value for plants cactus can survive for years in terrible soil but give cactus fertilizer it will grow as fast as grass & weeds. How long has it been since you feed your plants? When I lived in Phoenix it was very hard to find good fertilizer 4-2-2 palm tree fertilizer 1 lb for $10 is a rip off. Buy what is available with only a few house plants you don't need much.
I moved back to TN one 4" cactus grew to 7 ft tall in 2 years growing in the yard, it grew about 60 or 70 arms & 100s of beautiful spring time flowers. I gave it 15-15-15 fertilizer 50 lb bag is $15 plus nitrogen 50 lb bag is $10. My cactus got big and dangerous I cut it down.